1. Field of the Invention
This invention relates to wellhead apparatus, and in particular to apparatus for controlling the flow of fluids from a producing well.
2. Description of the Prior Art
The flow control of fluids from a producing well is complicated where debris is produced with the fluids. The debris, such as formation solids, pieces of well casing or well hardware and scale or corrosion products, also cause problems in other downstream equipment. Solids produced at a high velocity tend to erode valve seats, pipe walls and other materials they contact. Solids of appreciable size can become lodged in orifices or valve seats and thereby restrict fluid flow and in some cases render a throttling valve, orifice, or choke bean totally useless. Debris can also accumulate in many low points in the flow line causing flow restrictions and influencing corrosion and erosion rates.
The flow control of fluids from geothermal steam wells is particularly sensitive to the problem of flowing debris. Due to the relatively high velocity of the fluids produced, more and larger solids are entrained and produced. For example, some steam wells produce from several pounds to about 100 pounds of debris in a month. Practical flow control and downstream equipment performance can not be maintained without removal of the debris.
However, since the energy value of the geothermal fluids resides in their high pressure and temperature, any solids separation must be done with a minimal or preferably no pressure drop or temperature change. The smaller conventional filters tend to fill rapidly in this service, consequently restricting flow and increasing pressure drop. Larger conventional filters take longer to fill but have a much larger heat exchange surface and therefore can result in an undesirably high heat loss.
U.S. Pat. No. 2,855,048 to Jones discloses a removable tubular guard for a choke bean in an oil well Christmas tree. Solids produced with the fluids from an oil well are prevented from entering the choke bean by the perforated cylindrical guard. The guard can be periodically removed for replacement or cleaning. However, accumulation of solids in the device restricts the fluid flow and the well must be blocked in to clean the tubular guard. U.S. Pat. No. 3,939,659 to Matthews discloses a down-hole fluid filter for removing solids from a stream of fluid injected into the well to drive a down-hole pump. The filter can be flushed by remote control and the flushed solids are transported from the well with the produced fluids. Neither of these devices are adapted to adequately handle the large quantity of debris produced from a geothermal well and, in fact, the device of Matthews permits the introduction of additional debris into the produced fluid stream. Tubular guards or conventional fluid screens would be shattered and/or clogged by the produced debris due to the large mass and velocities of the debris. A need exists for a simple but effective wellhead apparatus for flow control of wells producing fluids and debris.
It is an object of this invention to provide wellhead apparatus for controlling the flow of fluids from a well producing fluid and debris.
Another object of this invention is to provide wellhead apparatus for controlling the flow of fluids from a well also producing a large quantity of debris by separating the debris from the fluid and throttling the flow of the debris-free fluid.
Yet another object of this invention is to provide a device for separating and accumulating a large quantity of debris flowing with the fluids from a well, without significantly restricting the flow therethrough and without a large heat loss, and thereby reduce the amount of maintenance required to maintain the well in operation.
Still another object of this invention is to provide wellhead apparatus to control the flow of fluids from a geothermal steam well producing a large quantity of debris at high velocities, without a significant loss in fluid pressure or temperature during the separation of the debris from the fluids.
Other objects and advantages of this invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings.